Centrifuges have many different types and the present invention is concerned with the two phase centrifuge type which provides high speed horizontal decanting that separate solids from liquids. Centrifuges of this type have been manufactured by United Oilfield Inc., who are assignees of the present application for a number of years and each includes three primary parts which are the base or skid, the stainless steel case mounted on the skid and the rotating assembly consisting of the bowl, auger and gearbox which assembly is mounted in the stationary steel case on the skid. The auger is mounted in the bowl so that the bowl surrounds the auger and both are mounted for coaxial rotation about a longitudinal axis. The auger comprises generally a cylindrical body coaxial to the cylindrical bowl with an auger flight on its outer surface which has an edge close to the inside surface of the cylindrical bowl.
To create the desired effect, the bowl with the auger inside rotates about the axis at slightly different speeds in the same direction. The bowl speed is variable depending upon the application and operating conditions.
During operation, feed slurry is fed from an axially extending stationary feed pipe at one end of the auger into a feed chamber at that end of the auger through an end wall of the bowl. The flowing slurry strikes an accelerator plate in the auger at one end of the feed chamber and is forced from the feed chamber outwardly into the bowl.
Centrifugal force causes heavier solids to accumulate on the inside surface of the bowl. The auger, which is rotating with the bowl but at a slow speed relative to the bowl, acts to continuously drag them axially along the bowl. Each of the bowl and the auger includes a tapered end portion at the feed end which converges radially inwardly toward a discharge end of the bowl, which is at the same end as the feed end. The rotation of the bowl and its tapered end tends to move the heavier material axially away from the discharge end to the cylindrical section of greater diameter. Thus the auger drags the material along the tapered section toward the discharge end. The discharge end includes discharge ports surrounding the feed duct so that the heavier solid material when it reaches the discharge end is discharged outwardly by the centrifugal force into the case for collection.
Finer solids are retained in the liquid traveling through the bowl away from the feed end to the remote end but are deposited on the wall of the bowl and are continuously removed as they build-up inside the bowl by the action of the auger and out the solids discharge ports.
Clean fluids travel towards the remote fluid end of the bowl and exit through adjustable eccentric ports at the remote fluid discharge end of the bowl. The centrifuge is commonly but not exclusively used for mud systems in drilling where the mud is re-circulated through the drill string to extract drilling solids so that the solids can be extracted in the centrifuge and the clean fluid from the centrifuge can be recycled back into the mud system of the operation.
The greatest difficulty in achieving optimal performance in a centrifuge of this type is wear caused by the combined corrosive nature of flow pressure and the abrasive solids on the steel structure of the centrifuge.